We plan to use a powerful new technology, massively parallel signature sequencing, to determine the complete transcriptomes (all mRNAs) of four hematopoietic stem cell populations, long-term hematopoietic stem cells (LT-HSC), short-term hematopoietic stem cells (ST-HSC), common lymphoid progenitor (CLP), and common myeloid progenitor (CMP), as well as the model hematopoietic cell line (EML-C1). We will place all of these identified genes (mRNAs) on DNA microarrays and oligonucleotide arrays to interrogate the gene expression patterns of selected hematopoietic stem cell populations. For example, we will employ gene knockout experiments to perturb an important signal transduction pathway in hematopoietic development, Wnt-beta-catenin, ion a cell line (EML-C1) using systems approaches. We will also use quantitative methods of proteomics to explore the protein expression patterns in hematopoietic stem cells and a progenitor cell line (EML-C1) using systems approaches. We will also use quantitative methods of proteomics to explore the protein expression patterns in hematopoietic stem cells and a progenitor cell line (EML-C1). We will identify orthologous and paralogous relationships between murine and Drosophila genes involved in stem cell biology. From these analyses will come a heightened understanding of the genes and informational pathways involved with murine hematopoietic stem cell self-renewal and development.